Background The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to all Bombardier, Inc., Model BD-100-1A10 airplanes. The NPRM was published in the Federal Register on July 2, 2025 (90 FR 28916). The NPRM was prompted by AD CF-2024-38, dated November 12, 2024 (Transport Canada AD CF-2024-38) (also referred to as the MCAI), issued by Transport Canada, which is the aviation authority for Canada. The MCAI states that Bombardier has been advised that the overhaul required by certificate maintenance requirement (CMR) task 27-40-00-104* was not fully completed on some units. As a result, some of the parts that were required to be replaced on the affected HSTAs as part of the overhauled task were re-installed in error. This condition, if not corrected, can lead to the failure of HSTA components, which can contribute to horizontal stabilizer surface disconnect at the actuator level and could lead to loss of continued safe flight and landing. In the NPRM, the FAA proposed to require verification of the HSTA serial number, and, if applicable, replacement of the HSTA. The FAA also proposed to prohibit the installation of affected parts under certain conditions. The FAA is issuing this AD to address the unsafe condition on these products. You may examine the MCAI in the AD docket at regulations.gov under Docket No. FAA-2025-1351. Discussion of Final Airworthiness Directive Comments The FAA received a comment from NetJets. The following presents the comment received on the NPRM and the FAA's response. Request To Clarify Requirement if Modification Plate Is Marked NetJets asked whether an affected HSTA, found during the proposed inspection or records review, would need to be replaced if its modification plate is marked with Moog Service Bulletin C47100-27-07, as specified in section 2.B. of Bombardier Service Bulletin 350-27-014. The FAA clarifies that an affected HSTA does not need to be replaced if it has a modification plate marked with Moog Service Bulletin C47100-27-07 because that marking indicates the part has already been properly reworked. The FAA recognizes that this relief is specified in paragraph 2.B.(4)(b) of the Bombardier service bulletin, and that Transport Canada AD CF-2024-38 allows installation of a part marked with the Moog service bulletin. Accordingly, the FAA has revised paragraph (h) of this AD to except any affected HSTA marked with the Moog service bulletin. Conclusion These products have been approved by the civil aviation authority of another country and are approved for operation in the United States. Pursuant to the FAA's bilateral agreement with this State of Design Authority, that authority has notified the FAA of the unsafe condition described in the MCAI referenced above. The FAA reviewed the relevant data, considered any comments received, and determined that air safety requires adopting this AD as proposed. Accordingly, the FAA is issuing this AD to address the unsafe condition on these products. Except for minor editorial changes, and any other changes described previously, this AD is adopted as proposed in the NPRM. None of the changes will increase the economic burden on any operator. Material Incorporated by Reference Under 1 CFR Part 51 The FAA reviewed the following Bombardier material: - Bombardier Service Bulletin 100-27-23, dated October 28, 2024; - Bombardier Service Bulletin 350-27-014, dated October 28, 2024. This material specifies procedures for verifying the HSTA serial number and, if applicable, corrective actions to include replacing the HSTA. These documents are distinct since they apply to different airplane configurations. This material is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in the ADDRESSES section. Costs of Compliance The FAA estimates that this AD affects 982 airplanes of U.S. registry. The FAA estimates the following costs to comply with this AD: Estimated Costs for Required Actions Labor cost Parts cost Cost per product Cost on U.S. operators Up to 2 work-hours × $85 per hour = Up to $170 $0 Up to $170 Up to $166,940. The FAA estimates the following costs to do any on-condition action that would be required based on the results of any required actions. The FAA has no way of determining the number of aircraft that might need this on-condition action: Estimated Costs of On-Condition Actions Labor cost Parts cost Cost per product 20 work-hours × $85 per hour = $1,700 $53,665 $55,365 The FAA has included all known costs in its cost estimate. According to the manufacturer, however, some or all of the costs of this AD may be covered under warranty, thereby reducing the cost impact on affected operators. Authority for This Rulemaking Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII: Aviation Programs, describes in more detail the scope of the Agency's authority. The FAA is issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701: General requirements. Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action. Regulatory Findings This AD will not have federalism implications under Executive Order 13132. This AD will not have a substantial direct effect on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. For the reasons discussed above, I certify that this AD: (1) Is not a "significant regulatory action" under Executive Order 12866, (2) Will not affect intrastate aviation in Alaska, and (3) Will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. List of Subjects in 14 CFR Part 39 Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. The Amendment Accordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows: PART 39-AIRWORTHINESS DIRECTIVES 1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. § 39.13 [Amended] 2. The FAA amends § 39.13 by adding the following new airworthiness directive: 2026-02-06 Bombardier, Inc.: Amendment 39-23242; Docket No. FAA-2025-1351; Project Identifier MCAI-2024-00667-T. (a) Effective Date This airworthiness directive (AD) is effective February 25, 2026. (b) Affected ADs None. (c) Applicability This AD applies to all Bombardier, Inc., Model BD-100-1A10 airplanes, certificated in any category. (d) Subject Air Transport Association (ATA) of America Code 27, Flight controls. (e) Unsafe Condition This AD was prompted by a report that some parts of horizontal stabilizer trim actuators (HSTAs) that were meant to be replaced through a required overhaul were not replaced and were instead reinstalled on the HSTAs. The FAA is issuing this AD to address HSTA parts that were not replaced as required. The unsafe condition, if not addressed, could result in the failure of HSTA components, which can contribute to horizontal stabilizer surface disconnect at the actuator level and could lead to loss of continued safe flight and landing. (f) Compliance Comply with this AD within the compliance times specified, unless already done. (g) Records Verification and Corrective Actions At the applicable time specified in figure 1 to paragraph (g) of this AD, do an inspection to determine the serial number of HSTA part number C47100-004 or C47100-005 in accordance with Section 2.B., Part A, of the Accomplishment Instructions of Bombardier Service Bulletin 100-27-23 or 350-27-014, both dated October 28, 2024, as applicable. A review of the airplane maintenance records is also acceptable provided the serial number of the HSTA can be conclusively determined from that review. Figure 1 to Paragraph ( g )-Compliance Time for Records Verification HSTA total flight hours accumulated as of the effective date of this AD Compliance time 10,000 or more Before accumulating 14,500 total flight hours on the HSTA, or before accumulating 7,500 total flight cycles on the HSTA, or within 24 months after the effective date of this AD, whichever occurs first. 9,700 or more but less than 10,000 Before accumulating 14,500 total flight hours on the HSTA, or before accumulating 7,500 total flight cycles on the HSTA, or within 36 months after the effective date of this AD, whichever occurs first. Less than 9,700 Before accumulating 14,500 total flight hours on the HSTA, or before accumulating 7,500 total flight cycles on the HSTA, or within 48 months after the effective date of this AD, whichever occurs first. (h) HSTA Replacement If, during the inspection or records review required by paragraph (g) of this AD, any HSTA having part number C47100-004 or C47100-005, with a serial number listed in Section 1.A. of Bombardier Service Bulletin 100-27-23 or 350-27-014, both dated October 28, 2024, as applicable is found: At the applicable time specified in figure 1 to paragraph (g) of this AD, replace the HSTA in accordance with Sections 2.C. and 2.D. of the Accomplishment Instructions of Bombardier Service Bulletin 100-27-23 or 350-27-014, both dated October 28, 2024, as applicable, unless the HSTA has a modification plate marked with Moog Service Bulletin C47100-27-07. (i) Parts Installation Limitation As of the effective date of this AD, no person may install, on any airplane, an HSTA, part number C47100-004 or C47100-005, with a serial number listed in Section 1.A. of Bombardier Service Bulletin 100-27-23 or 350-27-014, both dated October 28, 2024, unless the HSTA has a modification plate marked with Moog Service Bulletin C47100-27-07. (j) Additional AD Provisions The following provisions also apply to this AD: (1) Alternative Methods of Compliance (AMOCs): The Manager, International Validation Branch, FAA, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19. In accordance with 14 CFR 39.19, send your request to your principal inspector or responsible Flight Standards Office, as appropriate. If sending information directly to the manager of the International Validation Branch, send it to the attention of the person identified in paragraph (k) of this AD and email to: AMOC@faa.gov . Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the responsible Flight Standards Office. (2) Contacting the Manufacturer: For any requirement in this AD to obtain instructions from a manufacturer, the instructions must be accomplished using a method approved by the Manager, International Validation Branch, FAA; or Transport Canada; or Bombardier's Transport Canada Design Approval Organization (DAO). If approved by the DAO, the approval must include the DAO-authorized signature. (k) Additional Information For more information about this AD, contact John Massey, Aviation Safety Engineer, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590; phone: (516) 228-7300; email: 9-avs-nyaco-cos@faa.gov. (l) Material Incorporated by Reference (1) The Director of the Federal Register approved the incorporation by reference of the material listed in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51. (2) You must use this material as applicable to do the actions required by this AD, unless this AD specifies otherwise. (i) Bombardier Service Bulletin 100-27-23, dated October 28, 2024. (ii) Bombardier Service Bulletin 350-27-014, dated October 28, 2024. (3) For Bombardier material identified in this AD, contact Bombardier Business Aircraft Customer Response Center, 400 Côte-Vertu Road West, Dorval, Québec H4S 1Y9, Canada; telephone 514-855-2999; email ac.yul@aero.bombardier.com; website https://my.bombardier.com/. (4) You may view this material at the FAA, Airworthiness Products Section, Operational Safety Branch, 2200 South 216th St., Des Moines, WA. For information on the availability of this material at the FAA, call 206-231-3195. (5) You may view this material at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, visit www.archives.gov/federal-register/cfr/ibr-locations or email fr.inspection@nara.gov. Issued on January 14, 2026. Steven W. Thompson, Acting Deputy Director, Compliance & Airworthiness Division, Aircraft Certification Service.